Bullet holes in game engine?
You need the bullet hole to modify the texture applied to the material. That way it will never stick out!

An interesting approach may be to have multiple U,V vectors per object, and in the fragment shader, detect how close a fragment is to each of the U,V vectors, and if close enough, draw a bullet hole (maybe darken pixels as a function of distance between current U,V, and bullet hole U,V)

I am not sure how this is normally implemented in games however ;)